Since the outbreak of highly pathogenic H5NI avian influenza (Al) virus in Southeast Asia (SEA) in 2004, Thailand has been one of the main epidemic foci of human Al. Specific objectives are formulated as three subprojects, each having a series of specific aims that will contribute to our knowledge of Al epizoology and surveillance in SEA and, hence, may impact the prevention and control of Al at a global level. The recent Al outbreak and the presence of the poultry industry in these regions makes them ideal sites for assessment of likelihood of Al transmission (both low pathogenic (LP) and high pathogenic (HP)) to cullers, poultry farmers, and other high-risk occupational or recreational settings. The three subprojects and specific aims are: Subproject 1. Surveillance of Al virus in migratory and domestic bird populations and evaluation of their role in the spread of Al virus. Migratory birds are likely to play an important role in Al epidemic. The study aims at a comprehensive insight into the nature of Al infection of two major migratory bird species in Thailand. We will evaluate the role of these migratory birds for the spread of Al in Thailand. The data will help design appropriate measures to prevent Al transmission as well as measures for the conservation of wild birds. Subproject 2. Assessment of likelihood of symptomatic and asymptomatic Al infection of both LP and HP viruses in those who are exposed to Al in poultry and patients. Through active surveillance using serological assay, RT-PCR and viral isolation, we will assess infection rate, both symptomatic and asymptomatic, in people with exposure to infected poultry. We will also look for cases of human-to [unreadable] human transmission. We will also investigate all severe pneumonia cases in a specific location where Al has repeatedly occurred in order to get a full picture of Al and severe pneumonia in a population-based setting. These data will help understand the risk of Al infection in humans and design appropriate and effective preventive measures. Subproject 3. Genetic characterization of Al isolates to infer epidemiological insights and the nature of viral evolution. This subproject takes an opportunity of having viral isolates with systematically-collected epidemiological data to perform molecular epidemiological analyses from the viral sequences. The analyses will potentially tell us how the viruses spread, where the reservoirs of the viruses are, whether transmission chains are linked to certain epidemiological characteristics. We will also assess the evolution of the viral sequences and test whether there is a difference in the evolution between viruses in the natural host, duck, and viruses in other host species. If there is a difference, we will characterize the difference to learn about the mechanism by which influenza virus evolves into equilibrium with its natural host. The data will help us understand the nature of Al transmission among species and the perpetuation of epidemic in the region including monitoring and early warning system for new viral variants that may have a pandemic potential. [unreadable] [unreadable] [unreadable] [unreadable]